Systems are known which influence a mass flow, specifically a gas mass flow, in particular in connection with the control system of internal combustion engine. Examples of systems of this type are control systems for exhaust-gas recirculation, via which the mass flow of the exhaust gas is influenced by a control element, or valve control systems, which control the air mass flow to the internal combustion engine via an electrically controllable throttle valve. In each case, control elements are employed to control the mass flow. It has become clear that, over the course of operation, the line cross-section can become constricted as a result of contaminants. This is also the case in exhaust-gas recirculation systems that are cited as an example, in which, as a result of deposits of solid particles from the exhaust-gas and the intake system, the control valve and/or the line, over time, can be obstructed, and therefore the recycled exhaust-gas quantity can decrease as the operating time of the internal combustion engine increases. Then the control function of the internal combustion engine is no longer optimal. For this reason, it is important to monitor the functioning of a control system of this type and/or to take measures for adjusting the control system, which compensate for fault-based changes of this kind in the mass-flow throughput.
In connection with exhaust-gas recirculation valves, control concepts are known for compensating for changes of this type. From unpublished German Patent Application No. 100 41 073.1, dated Aug. 22, 2000 it is known that a modeled partial pressure of the recirculated exhaust gas is derived from the flow-rate characteristic curve of the exhaust-gas recirculation valve and an intake manifold pressure is modulated with the assistance of an independent filling signal and of the calculated internal residual gas pressure. This modeled intake manifold pressure is compared to the measured intake manifold pressure. The differences that arise, within certain parameters, are interpreted as errors in the flow-rate characteristic curve of the exhaust-gas recirculation valve, and correction values for this flow-rate characteristic curve are calculated. The type of correction values (slope correction, offset correction) is determined by the type of fault situation. In this manner, it is possible to effectively compensate for constrictions in the flow cross-section both at the valve and in the line. This known solution represents a closed control loop, which as a controlled variable uses the difference between the modeled and the measured intake manifold pressure variables, and as an actuating variable uses a position input to the valve, and as a controlling concept uses integral components. The monitoring, diagnosis, or adjustment of the control system is carried out by evaluating the control interventions, or the correction variables generated by the controller. Although a satisfactory correction and monitoring/diagnosis of the mass flow control system is achieved using the known solution, nevertheless the use of the closed control loop as well as of integrators, is associated with relatively greater expense and an undesirable inertia in the correction/diagnosis.
In German Published Patent Application No. 198 28 035, the calculation of inflowing and outflowing mass flows in the intake manifold of an internal combustion engine is described.